netdev - Re: [PATCH v6] net: batch skb dequeueing from softnet input_pkt

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Message-ID: <20100502213052.GB2673@gargoyle.fritz.box>
Date:	Sun, 2 May 2010 23:30:52 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>, hadi@...erus.ca,
	xiaosuo@...il.com, therbert@...gle.com, shemminger@...tta.com,
	netdev@...r.kernel.org, lenb@...nel.org
Subject: Re: [PATCH v6] net: batch skb dequeueing from softnet
	input_pkt_queue

On Sun, May 02, 2010 at 10:54:18AM -0700, Arjan van de Ven wrote:
> On Sun, 02 May 2010 16:27:28 +0200
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> > C2 latency seems to be 64  (us ?), while C1 seems to be 1
> 
> the processor_idle module has a "latency_factor" module parameter.
> The default is 2, but sometimes people think 6 is a better value...
> .. any chance you can try that value ?
> 
> Also, I'm starting to wonder if Andi's patch to use io_schedule() needs
> to be replaced with a net_schedule() kind of thing. The cpuidle code
> currently has a weight factor for IO (based on measuring/experiments),
> and maybe networking really needs another factor... so just having a
> parallel concept with a different weight could be the right answer for
> that.

We definitely need a net_schedule() for other reasons too: to avoid the blkio 
wait code and then also because networking needs a short "fast idle" timeout 
because the delays are not bounded.  

Otherwise a sender that suddenly stops sending could break all your power 
saving.

I think the reference count used in io_schedule is not the right model for 
this, probably needs a per cpu timeout ("be fast until this time"). Possibly 
a dynamic one feed by the measured input rate.

-Andi
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